# Python Enum Module

The `enum` module defines four enumeration classes that can be used to define unique sets of names and values: `Enum`, `IntEnum`, `Flag`, and `IntFlag`. It also defines one decorator, `unique`, and one helper, `auto`.

## Importing the Module

```python
import enum
```

## Creating an Enum

Enumerations are created using the `class` syntax, which makes them easy to read and write.

```python
from enum import Enum

class Color(Enum):
    RED = 1
    GREEN = 2
    BLUE = 3
```

## `auto()`

If the exact value is unimportant you can use `auto()`.

```python
from enum import Enum, auto

class Color(Enum):
    RED = auto()
    GREEN = auto()
    BLUE = auto()
```

## Iteration

You can iterate over the members of an enumeration.

```python
class Shape(Enum):
    SQUARE = 2
    DIAMOND = 4
    CIRCLE = 3

for shape in Shape:
    print(shape.name, shape.value)
```

## Comparisons

Enum members are compared by identity.

```python
if Shape.SQUARE is Shape.SQUARE:
    print("Identity comparison works")
```

## `IntEnum`

`IntEnum` is the same as `Enum`, but its members are also integers and can be compared to integers.

```python
from enum import IntEnum

class Shape(IntEnum):
    CIRCLE = 1
    SQUARE = 2

print(Shape.CIRCLE == 1) # True
```

## `Flag` and `IntFlag`

`Flag` and `IntFlag` are used to define enumerations that can be combined using bitwise operators.

```python
from enum import Flag, auto

class Color(Flag):
    RED = auto()
    GREEN = auto()
    BLUE = auto()
    WHITE = RED | GREEN | BLUE

print(Color.WHITE) # Color.WHITE
print(Color.RED in Color.WHITE) # True
```

## The `unique` Decorator

By default, enumerations allow aliases (multiple names for the same value). To disallow this, use the `@unique` decorator.

```python
from enum import Enum, unique

@unique
class Mistake(Enum):
    ONE = 1
    TWO = 2
    THREE = 3
    # FOUR = 3  # This would raise a ValueError
```

## Programmatic Access

You can access members by name or value.

```python
print(Color['RED'])  # Color.RED
print(Color(1))      # Color.RED (assuming RED=1)
```

[[programming/python/python]]